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Author Topic: Does a photon have mass equivalent to its energy?  (Read 25731 times)

Offline JP

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Re: Does a photon have mass equivalent to its energy?
« Reply #75 on: 25/05/2012 15:12:32 »
Thanks for the information, Pete.  It'll probably take me a while to wade through the links. 

You're right that I haven't done much work with general relativity/cosmology, which is where it sounds like relativistic mass finds use.  I'm much more familiar with quantum mechanics, where invariant mass is useful, and quantum optics, where invariant mass of single photons is zero. 

My general take on the subject was along the line of what Lightarrow said: that relativistic mass is just renaming energy, and we can use energy to do all the computations required without introducing a new name for it.  Is this true? 

My other general impression is that arguing over what should be called "mass" actually obscures a more important point: that when you transition from Newtonian physics to general relativity, there is no single quantity that has all the properties of Newtonian mass, so of course you can argue over the proper generalization of mass! 

The reason I take this track is that there's an analog that I do know well: in transitioning from classical to quantum mechanics, you can generalize the idea of classical trajectories to incorporate the wave nature of particles.  There are multiple ways of defining the quantum version of classical trajectories, and you usually pick one of those definitions based on whether its going to be useful in some computation (or useful in understanding a problem).  It would be silly to argue over which definition is "correct," since they all are correct models--the ones that have survived and been used are those which are useful.
 

Offline Pmb

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Re: Does a photon have mass equivalent to its energy?
« Reply #76 on: 25/05/2012 20:52:22 »
My general take on the subject was along the line of what Lightarrow said: that relativistic mass is just renaming energy, and we can use energy to do all the computations required without introducing a new name for it.  Is this true? 
Note: I use [math]E = \gammamc^2 [/math] = as inertial energy so as to distinguish it from W =  Energy = inertial energy + potentiual energy.

Answer to your question: No. Not in all generality. Then again what's in a name? The main thrust of my work has been to investigate all possible areas of application so as to find ways where people might make mistakes and seek out a way to describe it so that people won't make this mistakes - i.e. to raise awareness. I'm convince that inertial energy can be dispensed with and replaced by relativistic mass. So my question would then be - Why have two names for things when one can be replaced by the other. E.g.  inertial energy can be replaced wtih inertial mass in any concievable instance. So toss energy out. See my point? The proper mass people use that argument and neglect the other side to that argument.

This is like Hertz's views on force. He wrote a mechanics text and nowhere can the word "force" be found in it.

Keep in mind that inertial Energy and inertial mass are different conceptually. Why kill a concept? E.g just because I can write E = hf/c^2 it doesn't mean that we should replace E with hf/c^2 whenever we found it.

I just got home from a long luncheon. That caused a of pain and I'm just now trying to relax. How about I get back to the rest of this later tonight when I've had a chance to recover?

Please keep in mind that worrying about trivial things like definitions is very silly to me. Once each side provides their views then let it go is what I say. Unfortunately there was a lot for me to learn, things that nobody ever speaks about but which is very important. This lack of desire to learn is shameful. I'm saddened by people's lack of desire to learn about the relativistic mechanics of continuous systems in special relativity. This is where some very important stuff is learned.

What is your viewpoint of lifetime of particle vs proper life time of particle? Who really needs to define the lifetime of a particle when it's proportional to the proper lifetime of the particle. I can replace tthe later by the former can't I? :)
« Last Edit: 25/05/2012 21:45:41 by Pmb »
 

Offline Geezer

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Re: Does a photon have mass equivalent to its energy?
« Reply #77 on: 29/05/2012 01:17:44 »
It's amazing! No matter where you go on the internet there's always someone trying to force their views down your throat. It never ends!

Simple solution - stay off the internet, but what does that have to do with this thread?
 

Offline Pmb

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Re: Does a photon have mass equivalent to its energy?
« Reply #78 on: 30/05/2012 17:51:54 »
Thanks for the information, Pete.  It'll probably take me a while to wade through the links. 
You're most welcome! :)

You're right that I haven't done much work with general relativity/cosmology, which is where it sounds like relativistic mass finds use.
It's also used in basic relativity.  E.g. if somone wishes to ge a better understanding of the consequences of relativity in all its generality they need to understand the relativity of continuos media. There's a question aboiut it in Gravitation by Misner, Thorne and Wheeler. One good reason to study these things is to understand what others are saying in peer reviewed articles and to get the correct answer when your studying a text and are working on the problems.

I decided that I should post the answer to the question about the mass densiy of a magnetic field. It's at
http://home.comcast.net/~peter.m.brown/sr/mass_mag_field.htm

Quote
I'm much more familiar with quantum mechanics, where invariant mass is useful, and quantum optics, where invariant mass of single photons is zero.
I love QM. In a few months I might just refresh me QM. Grad school was a long time ago and even though I try to stay refreshed often it's just not enough unless you use of often. In the fall I'm sitting in on an EM course to refresh my EM. After that I'm hoping that there will be a QM course I can sit in. I need the exercise! :)

As I always say, use what is most useful at the time. People here got the impression that I never use proper mass in my work and leave the inertial mass out of it. Sometimes it's just easier. That seems to be the case for me, and of course others, when working on basic equations of particle physics balance equations. But when it came to working out the physics of cyclotron I found that inertial mass was easier for me. E.g.
http://home.comcast.net/~peter.m.brown/sr/cyclotron.htm

My general take on the subject was along the line of what Lightarrow said: that relativistic mass is just renaming energy, and we can use energy to do all the computations required without introducing a new name for it.  Is this true? 
No. It's not true. First off they are not the same thing. They're equivalent, not identical. And even then only in a limited use of the relationship. That use is the limitation to particle physics or any physics which is not a closed system. E.g. a drop of water in an electric field like, for example, an electrical storm. The electric field polarizes the drop of water. This leaves the drop in a state in which there is stress in the drop. This stress contributes to the inertia of the drop. In this case the relation E = mc2 is wrong. I thought I stated this when I quoted Mould's text Basic Relativity. Doesn't matter. I've been planing on creating a web page to describe such scenarios. I keep putting it off. Too lazy I guess.  I can send you an article in the inertia of stress if you'd like. It's very interesting.

My other general impression is that arguing over what should be called "mass" actually obscures a more important point: that when you transition from Newtonian physics to general relativity, there is no single quantity that has all the properties of Newtonian mass, so of course you can argue over the proper generalization of mass! 
My  philosophy is to use what works bestin all conceivable cases. Then use what is easier i the particular problem that you're working on. Myself? I have those damn subscripts all over the place. When using inertial mass the labeling can be a pain in the butt. Instead of m01 for the proper mass of particle one I can more easily use m01. It's much cleaner to look at. When things like this are employed all over then the entire derivation looks cleaner all over.

What really irritates me is when people constantly repeat themselves every single time I use inertial mass. That's quiet rude and that behaviour should be prohibited.

Here are a few derivtions that help explain my points. The main list his here
http://home.comcast.net/~peter.m.brown/

The page which lists all problems worked for SR is here
http://home.comcast.net/~peter.m.brown/sr/sr.htm

Here is the page on invariant mass. It demonstrates the uses and abuses of the concept. http://home.comcast.net/~peter.m.brown/sr/invariant_mass.htm

The term invariant mass is nomally used to apply to a system of non-interacting particles. The invariant mass is obtained using the 4-momentum 4-vector of the system. This 4-vector is calculated by summing up the 4-vectors of the particles. There is a hitch though. Normally when summing 4-vectors you have to evaluate them at the same point in spacetime. And also one has to make sure that the particles are no longer interacting. then the 4-vectors can be summed even though the 4-vectors are at different points in spacetime. Then you find the proper mass of this vector as you would a single particle. n the link these things are analyzed in detail.
« Last Edit: 30/05/2012 17:55:31 by Pmb »
 

Offline Pmb

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Re: Does a photon have mass equivalent to its energy?
« Reply #79 on: 30/05/2012 17:57:17 »
It's amazing! No matter where you go on the internet there's always someone trying to force their views down your throat. It never ends!
I'm dibled and can't get around much. I can only take so miuch TV. If I don't use my mind then I'll forget alot about the physics I know. I won't be challenged. The alternate is worse, hence my staying where the nuts are.

Simple solution - stay off the internet, but what does that have to do with this thread?
 

Offline yor_on

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Re: Does a photon have mass equivalent to its energy?
« Reply #80 on: 02/06/2012 16:32:53 »
Thinking of the original question. "If E =mc^2, and the photon transfers energy, how can it have no mass even if the mass is minuscule?"

One way of thinking of it may be to leave the concept of mass and instead consider tension and pressure. Then invariant proper mass and the photon share that ability. They both influence other particles, as well as get influenced by them.

The problem here being one of experience. We all differ between bosons and what we call matter, but as Pete pointed out, Einstein didn't. He called both EM and invariant proper mass 'matter'. And EM is defined through photons.
 

Offline JP

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Re: Does a photon have mass equivalent to its energy?
« Reply #81 on: 02/06/2012 17:09:44 »
. . . One way of thinking of it may be to leave the concept of mass and instead consider tension and pressure  . . .

My current opinion is that the best way to teach a lot of modern physics is to teach that classical ideas like "mass" or "particle" are useful approximations to more complex quantities like the stress-energy tensor or quantum wave/particles. 
 

Offline Pmb

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Re: Does a photon have mass equivalent to its energy?
« Reply #82 on: 02/06/2012 17:51:09 »
Thinking of the original question. "If E =mc^2, and the photon transfers energy, how can it have no mass even if the mass is minuscule?"

One way of thinking of it may be to leave the concept of mass and instead consider tension and pressure. Then invariant proper mass and the photon share that ability. They both influence other particles, as well as get influenced by them.

The problem here being one of experience. We all differ between bosons and what we call matter, but as Pete pointed out, Einstein didn't. He called both EM and invariant proper mass 'matter'. And EM is defined through photons.
photons are a quantum entity, not a classical one. SR and GR are classical physics, not quantum ones. And EM field is a classical field, not a quatum one. In classical mechanics one doesn't deal with photons.

I use photons in classic theory by never mixing quantum with classical. In SR/GR I use the luxon which is a particle whose energy is related to its momentm by E = pc and m = 0 (where m = proper mass). To see how to use it in an example please consider Einstein's box. See http://home.comcast.net/~peter.m.brown/sr/einsteins_box.htm

See Eq. (8). Does this help?

Antipa presented the idea of considering instead an atom that emits a photon and applies the center-of-mass theorem to the atom-photon system. This is dicussed in my page listed in the above link.
 

Offline lightarrow

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Re: Does a photon have mass equivalent to its energy?
« Reply #83 on: 02/06/2012 19:52:58 »
My general take on the subject was along the line of what Lightarrow said: that relativistic mass is just renaming energy, and we can use energy to do all the computations required without introducing a new name for it.  Is this true? 
No. It's not true. First off they are not the same thing. They're equivalent, not identical. And even then only in a limited use of the relationship. That use is the limitation to particle physics or any physics which is not a closed system. E.g. a drop of water in an electric field like, for example, an electrical storm. The electric field polarizes the drop of water. This leaves the drop in a state in which there is stress in the drop. This stress contributes to the inertia of the drop. In this case the relation E = mc2 is wrong.
That relation can't be wrong, if you consider the right system and compute the correct energy. For example, If an external field interacts with the drop, you can't pretend to apply the equation to the drop only.
 

Offline Pmb

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Re: Does a photon have mass equivalent to its energy?
« Reply #84 on: 02/06/2012 22:46:24 »
That relation can't be wrong, if you consider the right system ....
That's what it means when it is said that E = mc2only works under certain circumstances.
 

Offline lightarrow

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Re: Does a photon have mass equivalent to its energy?
« Reply #85 on: 03/06/2012 20:16:36 »
That relation can't be wrong, if you consider the right system ....
That's what it means when it is said that E = mc2only works under certain circumstances.
So your ojection that relativistic mass and energy are not the same, means that we have to specify which is the system and which is the energy?
It's a poor argument...
 

Offline Pmb

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Re: Does a photon have mass equivalent to its energy?
« Reply #86 on: 03/06/2012 22:04:32 »
So your ojection that relativistic mass and energy are not the same, means that we have to specify which is the system and which is the energy?
It's a poor argument...
That makes no sense. I already showed you a counter example which proved you wrong. Why are you making no attempt to show that the physics is wrong? You seem to think that this is something I created by my loansome. I didn't invent this by any stretch of the imagination. You can find this in the physics literature. Pick up Mould's text Basic Relativity and it will teach you the relavent physics. Or see Rindler's text. Or Moller's text. Or look through the literatuire such as the American Journal of Physics which is a  teaching journal. I can help you find your way around if you really want to.
 

Offline Pmb

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Re: Does a photon have mass equivalent to its energy?
« Reply #87 on: 04/06/2012 03:04:38 »
I finally found that paper on this topic I was referring to. There is an earlier paper than this by the same author but I'll have to start searching for that tomorrow.

The article is On the Inertial Mass Concept in Special Relativity by Mendel Sachs, Foundations of Physics Lectures, Vol. 1, No. 2, 1988
------------------
In this regard I have re-examined in an earlier paper the meaning of Einstein's energy-mass relation in special relativity

E = m0c2   (proper frame)


E = m0c2/[1 - (v/c)2 ]1/2   (moving frame)

demonstrating that, in the frame of the free particle with inertial mass m0, this equation does not signify that "energy is equivalent to mass", as it is usually asserted.
      What was pointed out earlier in this regard is that the concept of “energy” per se and the concept of “inertial mass” per se are, firstly, the same as they are in classical physics, and secondly, that they are logically different concepts: “energy is defined as the capacity of matter to do work  and “inertial mass” is defined as a quantification of the inertial property of matter, i.e. a measure of its resistance to a change of state of constant speed (or rest) with respect to any observer..
      Since these are entirely different concepts, energy cannot be said to be “equivalent to mass”.

------------------

which is exactly what I've been saying for years of course.
 

Offline yor_on

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Re: Does a photon have mass equivalent to its energy?
« Reply #88 on: 11/06/2012 13:51:33 »
I don't really know if Einstein used 'photons' as a description? I've seen people saying that he rather though of it as 'light quanta'? And the 'light quanta' definition naturally comes from black body radiation and the photo electric effect.. http://www.aip.org/history/einstein/essay-photoelectric.htm

Where the difference between that idea and the idea of a 'photon' goes may be discuss-able though? I like the idea of 'fields' myself in where what we call 'photons' are the fluctuations/emissions(?) measured by us. But I don't support waves either although the duality definitely exists. All as I then doesn't necessarily need to consider 'photons propagating'. And that's also the reason why I like the concept of indeterminacy better.

It's a very tricky subject.
« Last Edit: 11/06/2012 13:54:19 by yor_on »
 

Offline lightarrow

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Re: Does a photon have mass equivalent to its energy?
« Reply #89 on: 12/06/2012 12:21:10 »
I finally found that paper on this topic I was referring to. There is an earlier paper than this by the same author but I'll have to start searching for that tomorrow.

The article is On the Inertial Mass Concept in Special Relativity by Mendel Sachs, Foundations of Physics Lectures, Vol. 1, No. 2, 1988
------------------
In this regard I have re-examined in an earlier paper the meaning of Einstein's energy-mass relation in special relativity

E = m0c2   (proper frame)


E = m0c2/[1 - (v/c)2 ]1/2   (moving frame)

demonstrating that, in the frame of the free particle with inertial mass m0, this equation does not signify that "energy is equivalent to mass", as it is usually asserted.
      What was pointed out earlier in this regard is that the concept of “energy” per se and the concept of “inertial mass” per se are, firstly, the same as they are in classical physics, and secondly, that they are logically different concepts: “energy is defined as the capacity of matter to do work  and “inertial mass” is defined as a quantification of the inertial property of matter, i.e. a measure of its resistance to a change of state of constant speed (or rest) with respect to any observer..
      Since these are entirely different concepts, energy cannot be said to be “equivalent to mass”.

------------------

which is exactly what I've been saying for years of course.

I have coloured in blue the last sentence.
*Which* energy is he talking about there? Energy in the proper frame is a thing, energy in the other frame is another.
So, as you see, not even "Energy 1" is the same concept as "Energy 2"...
We were discussing if your relativistic mass is the same concept of total energy or not. It is.
 

Offline Pmb

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Re: Does a photon have mass equivalent to its energy?
« Reply #90 on: 15/06/2012 14:47:45 »
We were discussing if your relativistic mass is the same concept of total energy or not.
That wasn't the subject of the thread but a spin off topic. But yes, we discussed this. See the responses that I provided JP earlier in this thread
It is.
Is that supposed to be an argument? That is a useless statement.

I'm curious. Why do you think that you can simply claim the opposite and expect people to accept that as a factf? I'm sure that you know that it's not a valid argument tactic. People never believe that kind of thing.

That's a poor arguement tactic since its the universality of E = mc2 that is being challenged? Besides, I already provided proof that E = mc2 is not universally correct. If I recall correctly, you seemed to think that modifying the scenario at hand to a configuration where E = mc2 was true was a valid method of a counter proof. It is not. That was a logical fallacy known as a straw man argument.

See - http://en.wikipedia.org/wiki/Straw_man
Quote
A straw man is a type of argument and is an informal fallacy based on misrepresentation of an opponent's position. To "attack a straw man" is to create the illusion of having refuted a proposition by replacing it with a superficially similar yet unequivalent proposition (the "straw man"), and refuting it, without ever having actually refuted the original position.

Also, why did you refuse to answer my very direct question? I.e. see post #86
Quote
I already showed you a counter example which proved you wrong. Why are you making no attempt to show that the physics is wrong?

And if you really want to know which energy he' talking about then I'll send you the articles and you can read them. Taking snippets out of an article more than once is a good way to misunderstand the article.

It all you are able to do is to repeat yourself then we have nothing further to discuss. My counter example is proof enough that you're wrong. Anbybody can read an Mould's text and confirm this.
« Last Edit: 15/06/2012 15:05:01 by Pmb »
 

Offline Robro

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Re: Does a photon have mass equivalent to its energy?
« Reply #91 on: 25/06/2012 03:39:22 »
Mass from a photon should only be present as a result of the photon's bent path, the tighter the bend the greater the mass however minute it may be, but then a photon's path is never straight, it will forever bend through gravitational fields and also interact with the weak and strong forces from former to latter with increasing proportionality. There is a specific reason why matter can never travel faster than light, ergo, E does = MC squared, ***(NOT CUBED)***, as the electric plane and magnetic plane of a photon are opposed at 90 deg and do not form a sphere, and the field strength from a photon decreases proportionally as a square from the distance to the source. It's all just a piece of Pi.   
 

Offline LetoII

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Re: Does a photon have mass equivalent to its energy?
« Reply #92 on: 28/06/2012 11:13:01 »
i think the answer should be "potentially it does"
 

Offline Phractality

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Re: Does a photon have mass equivalent to its energy?
« Reply #93 on: 02/07/2012 05:54:24 »
I was going to put this response in the thread How "fast" does force "travel", but perhaps it belongs here, instead.

A supernova converts a significant fraction of a dying star's mass to energy (light and neutrinos) in a matter of hours, and that energy radiates at the speed of light.

If that energy has no gravitational mass, the gravity felt here from that star should drop after a speed-of-gravity delay. If the force of gravity propagates instantaneously, the gravity should drop when the supernova happens, not when we see it. If the speed of gravity is the speed of light, the gravity should drop here when we see the supernova.

On the other hand, if the energy does have gravitational mass, which forms a uniform spherical shell of light and neutrinos, and gravity propagates instantaneously, then Newton's shell theorem is applicable. (The shell theorem tacitly assumes that gravity is instantaneous at all distances.) According to the shell theorem, gravity outside a uniform spherical shell of matter (due to the presence of that matter) is inversely proportional to the distance from the center of the sphere, and gravity inside the sphere (due to the presence of that matter) is zero. As the spherical shell of energy leaves the supernova it would continue to exert the same gravity on us as it did before the matter was converted to energy. As soon as the supernova becomes visible, we enter the spherical shell and the gravity from that spherical shell of matter drops to zero in the time it takes for the light and neutrinos of the supernova to fade from our view.

So, when matter is converted to energy, the drop in gravity should occur after a speed-of-light delay. The only way it can occur instantaneously is if A: gravity propagates instantaneously, and B: energy has no gravitational mass.

Of course, all this is moot, since the drop in gravity would be too minute to be detected by our instruments. Perhaps it could be detected as a change in the trajectories of the supernova's neighbor stars during the time after the supernova occurs and before it becomes visible at the locations of those neighbor stars.

If the supernova's energy does not radiate uniformly in a spherical shell, then the shell theorem is not applicable.
« Last Edit: 02/07/2012 05:56:23 by Phractality »
 

Offline Robro

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Re: Does a photon have mass equivalent to its energy?
« Reply #94 on: 05/07/2012 07:09:21 »
Let's assume for a moment that mass is a condition exhibited by a photons bent path as it completes it's saturation of maximum amplitude toward increasing electromagnetic field strength in space. Light does have the potential to show mass equal to it's energy. An electron will show the same amount of energy as a photon that has a wavelength equal to the circumference of the electron. This implies that all of matter is made of electromagnetism, as photons locked in their own fields to become points measured as particles.  Forget all the pseudo science out there that includes thoughts of extra dimensions, worm holes, everything's from nothings and the like. There is a specific reason why matter cannot travel faster than light. Mass is a property of light. Light does not travel faster than light.
« Last Edit: 05/07/2012 07:18:19 by Robro »
 

Offline yor_on

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Re: Does a photon have mass equivalent to its energy?
« Reply #95 on: 05/07/2012 13:30:24 »
I think of it as a field, consisting of all mass there is. In that (dynamic) field all updates on 'gravity' should propagate at 'c'. That means that if you have a star going supernova, radiating away a lot of energy, you won't notice a difference until the information has reached us, and it should be gradual as the radiation pass us by. As I think of it that is :)

The field is instantaneous if one mean that it is 'everywhere', but the information exchange about its equilibrium should obey 'c'.
 

Offline yor_on

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Re: Does a photon have mass equivalent to its energy?
« Reply #96 on: 05/07/2012 13:55:01 »
 Maybe I should change this a little to get my idea through :)

Think of a static field. That is 'gravity', without a arrow. The arrow and mass/energy/motion translate this static field into a dynamic field that always must find its equilibrium, in each instant of 'the arrow of time', but to us ever so weakly changing if we now could measure it.

But ignoring 'the arrow' the field is static, and always in a equilibrium. And that may sound weird as we should be able to assume that if something 'change' then there must be moments of unbalance, but we're speaking of a whole 'SpaceTime' now and I doubt it ever can be found to be unbalanced, changing under the arrow yes, but always in a equilibrium. And that sounds weird, doesn't it :)
 

Offline Robro

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Re: Does a photon have mass equivalent to its energy?
« Reply #97 on: 06/07/2012 01:03:58 »
I am wondering; By what 'means' does the presence of mass curve space/time? And, how exactly is space linked to time?
 

Offline yor_on

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Re: Does a photon have mass equivalent to its energy?
« Reply #98 on: 07/07/2012 00:16:15 »
The metric of space is 'gravity' according to Einstein. What that means, my view, is that there can be no 'space' without gravity existent. Gravity change 'time rates' if compared between frames of reference, as proven on Earth by NIST at as short distances as decimeters. Special relativity doesn't discuss this but General relativity does, all as I see it :)

As for how mass distorts space?

That one is a tough one to answer. It follows as a logical conclusion from general relativity and light as a constant and it has recently been tested by gravity probe B if i remember right, and there found to distort the space around Earth. Then you also have the other experiments proving it, in fact it was one of the first real proofs of relativity as i remember. But how? I don't really know. It also depends on what 'space' is.

What is a vacuum/space made of ? :)

Nothing? Or something?
Why do we expect 'bosons' as the Higgs particle to exist, although in themselves unmeasurable to us?
Maybe because it possibly could describe the 'why and how'  of that distortion existence? Although I'm not sure at all of how that would be explained just by us expecting the 'Higgs syrup'? And to that you can add how the Higgs particle then should be related to measuring 'time rates' between frames of reference, as that too is proven to exist. And as mass is coupled to gravity?

Myself I do think we have a lot of 'unmeasurabels' around :) although I'm not sure on the Higgs theory as a 'particle'. I prefer 'fields' myself. As for photons and EM, they don't bend to a EM-field. Depending on hypothesis you might explain that but experimentally they never have, as far as I know.
 

The Naked Scientists Forum

Re: Does a photon have mass equivalent to its energy?
« Reply #98 on: 07/07/2012 00:16:15 »

 

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